In general, the exhaust gas of an automobile contains large quantities of harmful substances including carbon monoxides, nitrogen oxides, and hydrocarbons. While the production of harmful substances such as nitrogen oxides often increases in quantity with the temperature of an engine, EGR (Exhaust Gas Recirculation) is used to decrease such harmful substances by recirculating exhaust gas into an intake system and lowering the combustion temperature in a cylinder. In many EGR processes, an EGR cooler is installed that is intended to cool high-temperature exhaust gas with cooling water.
FIG. 1 is a vertical cross-sectional view illustrating an EGR cooler according to the prior art. As illustrated in FIG. 1, the EGR cooler is comprised of a cylindrical cell 1, plates 2 installed at both ends of the cell 1 to close both ends of the cell 1, and a plurality of tubes 3 that penetrate through the plates 2 and extend and are installed in the internal shaft center of the cell 1. Here, the cell 1 is furnished with a cooling water inlet 4 and a cooling water outlet 5 at its two sides so that cooling water 9 introduced from the cooling water inlet 4 can move along the exterior of the tubes 3 and can be discharged through the cooling water outlet 5. In addition, tanks 6 on which an exhaust gas inlet 7 and an exhaust gas outlet 8 are formed, respectively, are installed at each end of the cell 1 so that exhaust gas 10 introduced from the exhaust gas inlet 7 can exchange heat with the cooling water 9, and can then be discharged through the exhaust gas outlet 8.
However, as exhaust gas undergoes horizontal movement through straight tubes in EGR coolers according to the prior art, effective contact between the tubes and cooling water often does not take place, and the time allowed for heat exchange therebetween becomes short. Consequently, heat transfer to the cooling water that moves around the exhaust gas and the tubes often does not take place effectively. As a result, heat exchange efficiency can suffer remarkably.
In addition, in the event that the flow of exhaust gas becomes weak in the tubes, soot and other material in the exhaust gas can accumulate in flow pathways, thereby interfering with the flow of exhaust gas. Furthermore, existing straight EGR coolers can restrict positioning and installation of other parts in a vehicle, where space is typically at a premium. Such restrictions can negatively impact the efficient and effective positioning and installation of parts within a vehicle.